The present invention relates to power supplies, and more particularly to power supplies with multiple input voltage sources.
The use of power supplies with multiple input voltage sources, in industries such as the telecommunications industry, is well known in the art. Power supplies with multiple input voltage sources provide redundancy in the system to ensure that power continues to be provided to the system, even when one of the voltage sources fail.
FIG. 1 illustrates a conventional multiple input voltage sources power supply circuit. The circuit 100 comprises a first voltage source 102 coupled in series to a first diode 106, a second voltage source 104 coupled in series to a second diode 108. The cathodes of the diodes 106 and 108 are coupled directly to the voltage sources 102 and 104, respectively, and the anodes of the diodes 106 and 108 are connected to the load 110, which is generally a DC-DC regulator.
When the first voltage source 102 is xe2x80x9conxe2x80x9d, i.e., supplying a voltage, such as xe2x88x9248V, and the second voltage source 104 is xe2x80x9coffxe2x80x9d, i.e., either supplying less than xe2x88x9248V or not connected, then xe2x88x9248V is supplied to the load 110 by the first voltage source 102 because the second diode 108 is back biased. The second diode 108 prevents current from back flowing to the second voltage source 104, and thus prevents the second voltage source 104 from becoming a sink and overheating the power supply.
When the first voltage source 102 is xe2x80x9coffxe2x80x9d, i.e., either supplying a voltage less than xe2x88x9248V or not connected, and the second voltage source 104 is xe2x80x9conxe2x80x9d, i.e., supplying xe2x88x9248V, then xe2x88x9248V is supplied to the load 110 by the second voltage source 104. The first diode 106 prevents current from back flowing to the first voltage source 102 because the first diode 106 is back biased, and thus preventing the first voltage source 102 from becoming a sink. Other voltage sources may be coupled to the load 110 and function in the same manner.
However, the loss of power in each diode 106 and 108 is significant for high powered loads. For example, for voltage sources which supply xe2x88x9248V, the loss per diode 106 or 108 could be as high as 10W for a 1 kW load. The conventional multiple input voltage sources power supply is thus inefficient.
Accordingly, there exists a need for a high efficiency multiple input voltage sources power supply. The power supply should provide higher efficiency than a conventional power supply and at the same time, provide a means for preventing current flow among different voltage sources connected to a common load. The present invention addresses such a need.
The present invention provides a highly efficient power supply with redundant multiple input voltage sources. The power supply uses switching transistors, specifically MOSFET""s, to create paths for current from one of the voltage sources to the load. The switching transistors are switched either xe2x80x9conxe2x80x9d or xe2x80x9coffxe2x80x9d by comparators which compare the output from the voltage sources. These comparators allow the highest voltage source to provide power to the load, and keep the other switching transistors xe2x80x9coffxe2x80x9d that connect the common load to other voltage sources. Because the switching transistors have lower conduction losses than diodes in conventional power supplies, the power supply in accordance with the present invention is more efficient.